view src/share/vm/memory/genMarkSweep.cpp @ 453:c96030fff130

6684579: SoftReference processing can be made more efficient Summary: For current soft-ref clearing policies, we can decide at marking time if a soft-reference will definitely not be cleared, postponing the decision of whether it will definitely be cleared to the final reference processing phase. This can be especially beneficial in the case of concurrent collectors where the marking is usually concurrent but reference processing is usually not. Reviewed-by: jmasa
author ysr
date Thu, 20 Nov 2008 16:56:09 -0800
parents 1ee8caae33af
children 27a80744a83b
line wrap: on
line source
/*
 * Copyright 2001-2008 Sun Microsystems, Inc.  All Rights Reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
 * CA 95054 USA or visit www.sun.com if you need additional information or
 * have any questions.
 *
 */

#include "incls/_precompiled.incl"
#include "incls/_genMarkSweep.cpp.incl"

void GenMarkSweep::invoke_at_safepoint(int level, ReferenceProcessor* rp,
  bool clear_all_softrefs) {
  assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint");

  // hook up weak ref data so it can be used during Mark-Sweep
  assert(ref_processor() == NULL, "no stomping");
  assert(rp != NULL, "should be non-NULL");
  _ref_processor = rp;
  rp->snap_policy(clear_all_softrefs);

  TraceTime t1("Full GC", PrintGC && !PrintGCDetails, true, gclog_or_tty);

  // When collecting the permanent generation methodOops may be moving,
  // so we either have to flush all bcp data or convert it into bci.
  CodeCache::gc_prologue();
  Threads::gc_prologue();

  // Increment the invocation count for the permanent generation, since it is
  // implicitly collected whenever we do a full mark sweep collection.
  GenCollectedHeap* gch = GenCollectedHeap::heap();
  gch->perm_gen()->stat_record()->invocations++;

  // Capture heap size before collection for printing.
  size_t gch_prev_used = gch->used();

  // Some of the card table updates below assume that the perm gen is
  // also being collected.
  assert(level == gch->n_gens() - 1,
         "All generations are being collected, ergo perm gen too.");

  // Capture used regions for each generation that will be
  // subject to collection, so that card table adjustments can
  // be made intelligently (see clear / invalidate further below).
  gch->save_used_regions(level, true /* perm */);

  allocate_stacks();

  mark_sweep_phase1(level, clear_all_softrefs);

  mark_sweep_phase2();

  // Don't add any more derived pointers during phase3
  COMPILER2_PRESENT(assert(DerivedPointerTable::is_active(), "Sanity"));
  COMPILER2_PRESENT(DerivedPointerTable::set_active(false));

  mark_sweep_phase3(level);

  VALIDATE_MARK_SWEEP_ONLY(
    if (ValidateMarkSweep) {
      guarantee(_root_refs_stack->length() == 0, "should be empty by now");
    }
  )

  mark_sweep_phase4();

  VALIDATE_MARK_SWEEP_ONLY(
    if (ValidateMarkSweep) {
      guarantee(_live_oops->length() == _live_oops_moved_to->length(),
                "should be the same size");
    }
  )

  restore_marks();

  // Set saved marks for allocation profiler (and other things? -- dld)
  // (Should this be in general part?)
  gch->save_marks();

  deallocate_stacks();

  // If compaction completely evacuated all generations younger than this
  // one, then we can clear the card table.  Otherwise, we must invalidate
  // it (consider all cards dirty).  In the future, we might consider doing
  // compaction within generations only, and doing card-table sliding.
  bool all_empty = true;
  for (int i = 0; all_empty && i < level; i++) {
    Generation* g = gch->get_gen(i);
    all_empty = all_empty && gch->get_gen(i)->used() == 0;
  }
  GenRemSet* rs = gch->rem_set();
  // Clear/invalidate below make use of the "prev_used_regions" saved earlier.
  if (all_empty) {
    // We've evacuated all generations below us.
    Generation* g = gch->get_gen(level);
    rs->clear_into_younger(g, true /* perm */);
  } else {
    // Invalidate the cards corresponding to the currently used
    // region and clear those corresponding to the evacuated region
    // of all generations just collected (i.e. level and younger).
    rs->invalidate_or_clear(gch->get_gen(level),
                            true /* younger */,
                            true /* perm */);
  }

  Threads::gc_epilogue();
  CodeCache::gc_epilogue();

  if (PrintGC && !PrintGCDetails) {
    gch->print_heap_change(gch_prev_used);
  }

  // refs processing: clean slate
  _ref_processor = NULL;

  // Update heap occupancy information which is used as
  // input to soft ref clearing policy at the next gc.
  Universe::update_heap_info_at_gc();

  // Update time of last gc for all generations we collected
  // (which curently is all the generations in the heap).
  gch->update_time_of_last_gc(os::javaTimeMillis());
}

void GenMarkSweep::allocate_stacks() {
  GenCollectedHeap* gch = GenCollectedHeap::heap();
  // Scratch request on behalf of oldest generation; will do no
  // allocation.
  ScratchBlock* scratch = gch->gather_scratch(gch->_gens[gch->_n_gens-1], 0);

  // $$$ To cut a corner, we'll only use the first scratch block, and then
  // revert to malloc.
  if (scratch != NULL) {
    _preserved_count_max =
      scratch->num_words * HeapWordSize / sizeof(PreservedMark);
  } else {
    _preserved_count_max = 0;
  }

  _preserved_marks = (PreservedMark*)scratch;
  _preserved_count = 0;
  _preserved_mark_stack = NULL;
  _preserved_oop_stack = NULL;

  _marking_stack       = new (ResourceObj::C_HEAP) GrowableArray<oop>(4000, true);

  int size = SystemDictionary::number_of_classes() * 2;
  _revisit_klass_stack = new (ResourceObj::C_HEAP) GrowableArray<Klass*>(size, true);

#ifdef VALIDATE_MARK_SWEEP
  if (ValidateMarkSweep) {
    _root_refs_stack    = new (ResourceObj::C_HEAP) GrowableArray<void*>(100, true);
    _other_refs_stack   = new (ResourceObj::C_HEAP) GrowableArray<void*>(100, true);
    _adjusted_pointers  = new (ResourceObj::C_HEAP) GrowableArray<void*>(100, true);
    _live_oops          = new (ResourceObj::C_HEAP) GrowableArray<oop>(100, true);
    _live_oops_moved_to = new (ResourceObj::C_HEAP) GrowableArray<oop>(100, true);
    _live_oops_size     = new (ResourceObj::C_HEAP) GrowableArray<size_t>(100, true);
  }
  if (RecordMarkSweepCompaction) {
    if (_cur_gc_live_oops == NULL) {
      _cur_gc_live_oops           = new(ResourceObj::C_HEAP) GrowableArray<HeapWord*>(100, true);
      _cur_gc_live_oops_moved_to  = new(ResourceObj::C_HEAP) GrowableArray<HeapWord*>(100, true);
      _cur_gc_live_oops_size      = new(ResourceObj::C_HEAP) GrowableArray<size_t>(100, true);
      _last_gc_live_oops          = new(ResourceObj::C_HEAP) GrowableArray<HeapWord*>(100, true);
      _last_gc_live_oops_moved_to = new(ResourceObj::C_HEAP) GrowableArray<HeapWord*>(100, true);
      _last_gc_live_oops_size     = new(ResourceObj::C_HEAP) GrowableArray<size_t>(100, true);
    } else {
      _cur_gc_live_oops->clear();
      _cur_gc_live_oops_moved_to->clear();
      _cur_gc_live_oops_size->clear();
    }
  }
#endif
}


void GenMarkSweep::deallocate_stacks() {

  if (!UseG1GC) {
    GenCollectedHeap* gch = GenCollectedHeap::heap();
    gch->release_scratch();
  }

  if (_preserved_oop_stack) {
    delete _preserved_mark_stack;
    _preserved_mark_stack = NULL;
    delete _preserved_oop_stack;
    _preserved_oop_stack = NULL;
  }

  delete _marking_stack;
  delete _revisit_klass_stack;

#ifdef VALIDATE_MARK_SWEEP
  if (ValidateMarkSweep) {
    delete _root_refs_stack;
    delete _other_refs_stack;
    delete _adjusted_pointers;
    delete _live_oops;
    delete _live_oops_size;
    delete _live_oops_moved_to;
    _live_oops_index = 0;
    _live_oops_index_at_perm = 0;
  }
#endif
}

void GenMarkSweep::mark_sweep_phase1(int level,
                                  bool clear_all_softrefs) {
  // Recursively traverse all live objects and mark them
  EventMark m("1 mark object");
  TraceTime tm("phase 1", PrintGC && Verbose, true, gclog_or_tty);
  trace(" 1");

  VALIDATE_MARK_SWEEP_ONLY(reset_live_oop_tracking(false));

  GenCollectedHeap* gch = GenCollectedHeap::heap();

  // Because follow_root_closure is created statically, cannot
  // use OopsInGenClosure constructor which takes a generation,
  // as the Universe has not been created when the static constructors
  // are run.
  follow_root_closure.set_orig_generation(gch->get_gen(level));

  gch->gen_process_strong_roots(level,
                                false, // Younger gens are not roots.
                                true,  // Collecting permanent generation.
                                SharedHeap::SO_SystemClasses,
                                &follow_root_closure, &follow_root_closure);

  // Process reference objects found during marking
  {
    ref_processor()->snap_policy(clear_all_softrefs);
    ref_processor()->process_discovered_references(
      &is_alive, &keep_alive, &follow_stack_closure, NULL);
  }

  // Follow system dictionary roots and unload classes
  bool purged_class = SystemDictionary::do_unloading(&is_alive);

  // Follow code cache roots
  CodeCache::do_unloading(&is_alive, &keep_alive, purged_class);
  follow_stack(); // Flush marking stack

  // Update subklass/sibling/implementor links of live klasses
  follow_weak_klass_links();
  assert(_marking_stack->is_empty(), "just drained");

  // Visit symbol and interned string tables and delete unmarked oops
  SymbolTable::unlink(&is_alive);
  StringTable::unlink(&is_alive);

  assert(_marking_stack->is_empty(), "stack should be empty by now");
}


void GenMarkSweep::mark_sweep_phase2() {
  // Now all live objects are marked, compute the new object addresses.

  // It is imperative that we traverse perm_gen LAST. If dead space is
  // allowed a range of dead object may get overwritten by a dead int
  // array. If perm_gen is not traversed last a klassOop may get
  // overwritten. This is fine since it is dead, but if the class has dead
  // instances we have to skip them, and in order to find their size we
  // need the klassOop!
  //
  // It is not required that we traverse spaces in the same order in
  // phase2, phase3 and phase4, but the ValidateMarkSweep live oops
  // tracking expects us to do so. See comment under phase4.

  GenCollectedHeap* gch = GenCollectedHeap::heap();
  Generation* pg = gch->perm_gen();

  EventMark m("2 compute new addresses");
  TraceTime tm("phase 2", PrintGC && Verbose, true, gclog_or_tty);
  trace("2");

  VALIDATE_MARK_SWEEP_ONLY(reset_live_oop_tracking(false));

  gch->prepare_for_compaction();

  VALIDATE_MARK_SWEEP_ONLY(_live_oops_index_at_perm = _live_oops_index);
  CompactPoint perm_cp(pg, NULL, NULL);
  pg->prepare_for_compaction(&perm_cp);
}

class GenAdjustPointersClosure: public GenCollectedHeap::GenClosure {
public:
  void do_generation(Generation* gen) {
    gen->adjust_pointers();
  }
};

void GenMarkSweep::mark_sweep_phase3(int level) {
  GenCollectedHeap* gch = GenCollectedHeap::heap();
  Generation* pg = gch->perm_gen();

  // Adjust the pointers to reflect the new locations
  EventMark m("3 adjust pointers");
  TraceTime tm("phase 3", PrintGC && Verbose, true, gclog_or_tty);
  trace("3");

  VALIDATE_MARK_SWEEP_ONLY(reset_live_oop_tracking(false));

  // Needs to be done before the system dictionary is adjusted.
  pg->pre_adjust_pointers();

  // Because the two closures below are created statically, cannot
  // use OopsInGenClosure constructor which takes a generation,
  // as the Universe has not been created when the static constructors
  // are run.
  adjust_root_pointer_closure.set_orig_generation(gch->get_gen(level));
  adjust_pointer_closure.set_orig_generation(gch->get_gen(level));

  gch->gen_process_strong_roots(level,
                                false, // Younger gens are not roots.
                                true,  // Collecting permanent generation.
                                SharedHeap::SO_AllClasses,
                                &adjust_root_pointer_closure,
                                &adjust_root_pointer_closure);

  // Now adjust pointers in remaining weak roots.  (All of which should
  // have been cleared if they pointed to non-surviving objects.)
  gch->gen_process_weak_roots(&adjust_root_pointer_closure,
                              &adjust_pointer_closure);

  adjust_marks();
  GenAdjustPointersClosure blk;
  gch->generation_iterate(&blk, true);
  pg->adjust_pointers();
}

class GenCompactClosure: public GenCollectedHeap::GenClosure {
public:
  void do_generation(Generation* gen) {
    gen->compact();
  }
};

void GenMarkSweep::mark_sweep_phase4() {
  // All pointers are now adjusted, move objects accordingly

  // It is imperative that we traverse perm_gen first in phase4. All
  // classes must be allocated earlier than their instances, and traversing
  // perm_gen first makes sure that all klassOops have moved to their new
  // location before any instance does a dispatch through it's klass!

  // The ValidateMarkSweep live oops tracking expects us to traverse spaces
  // in the same order in phase2, phase3 and phase4. We don't quite do that
  // here (perm_gen first rather than last), so we tell the validate code
  // to use a higher index (saved from phase2) when verifying perm_gen.
  GenCollectedHeap* gch = GenCollectedHeap::heap();
  Generation* pg = gch->perm_gen();

  EventMark m("4 compact heap");
  TraceTime tm("phase 4", PrintGC && Verbose, true, gclog_or_tty);
  trace("4");

  VALIDATE_MARK_SWEEP_ONLY(reset_live_oop_tracking(true));

  pg->compact();

  VALIDATE_MARK_SWEEP_ONLY(reset_live_oop_tracking(false));

  GenCompactClosure blk;
  gch->generation_iterate(&blk, true);

  VALIDATE_MARK_SWEEP_ONLY(compaction_complete());

  pg->post_compact(); // Shared spaces verification.
}